The oxidation of ortho-xylene to phthalic anhydride is known. The reactant ratios, conditions and other parameters shown in the art are substantially unchanged. The present invention is the discovery of a particular group of catalysts that are especially effective in this reaction. The catalysts are very easy to prepare; they give smooth temperature control and high per pass conversions.
U.S. Pat. No. 3,464,930 discloses use of a catalyst containing vanadium and titanium coated on nonporous, inert materials, i.e., materials free from pores or having a small surface area, preferably less than 3 sq. m./g. This patent discloses the preparation of a catalyst containing the oxides of titanium and vanadium by pretreating a carrier of fused aluminum oxide with titanium tetrachloride and glacial acetic acid and bringing this carrier in contact with a paste comprising vanadium oxalate and anatase.
British Pat. No. 1,140,264 is an equivalent of U.S. Pat. No. 3,464,930.
British Pat. No. 1,203,321, a Patent of Addition to No. 1,140,264, discloses oxidation catalysts which are an improvement over the oxidation catalysts containing vanadium pentoxide and titanium dioxide in British Pat. No. 1,140,264. British Pat. No. 1,203,321 discloses that the coating on catalysts which have been coated with the composition containing vanadium pentoxide and titanium dioxide by applying the composition in a dissolved or suspended form to a carrier which has been heated to a temperature of 160.degree. to 500.degree. C. has greater strength. The object of this invention is to overcome the disadvantage in British Pat. No. 1,140,264 of resistance to abrasion.
British Pat. No. 1,237,954 discloses the air oxidation of o-xylene in a tubular reactor at an elevated temperature in contact with a fixed-bed catalyst comprising a nonporous carrier having a coating of a composition containing vanadium oxide and titanium oxide. The object of this invention is to overcome the disadvantage of catalyst discoloration in British Pat. No. 1,140,264.
British Pat. No. 1,238,379 discloses use of supported catalysts containing titanium dioxide, vanadium pentoxide and aluminum oxide, lithium oxide and/or zirconium dioxide coated on an inert nonporous carrier. The object of this invention is to overcome the disadvantage in British Pat. No. 1,140,264, wherein the catalyst does not achieve their optimum effect until after a certain operational period.
British Pat. No. 1,267,043 discloses the use of catalysts containing vanadium pentoxide, titanium dioxide and a phosphorus compound coated on nonporous inert carriers. The object of this invention is to improve the life of catalysts such as those described in British Pat. No. 1,140,264.
Only unexpected results are obtained using novel catalysts of the invention for the production of phthalic anhydride.